It's hard for a traditionalist (not a Luddite) to fully deal with the premise of wikis as documents that anyone can update, add to, change, etc. I know there are permissions and such, but anyone?? I'm reminded of the example I used to use when teaching about how to determine the trustworthyness of a web site -- I have a cocker spaniel, and there's nothing stopping me from putting up a web site purporting that I am the world's foremost authority and advisor on cocker spaniels, but should you trust my site or the one put up by a veterinarian?
That said -- what a wonderful thing wikis are! I like the Princeton Public Library's Book Lovers wiki, and I learned some useful things from Bull Run Public Library's wiki. (Common Craft is a great resource!) Both of these projects exemplify the "put your 2 cents in" purpose of wikis. And, the Stevens County wiki project -- build a "home-grown" Stevens County encyclopedia -- is good to explore; it includes history, guidebooks, advertisements, and other relevant information about a rural area for which such a rich compilation might not otherwise exist.